CCIE: between 4,500 and 5,000, extrapolating from a 3,000 number published mid-last-year (as of 3/31/2002)
CCDA: I can't find any published numbers, but since the CCNA is highly recommended and it's only a single-exam cert, I'm guessing this population is in excess of 10,000. I've put an inquiry into Cisco to see if I can get some better numbers for you.
CISSP: ~6,000 (as of 12/31/2001, as covered in the isc2's 2001 annual report at www.isc2.org)
For numbers on MS certifications, check the bottom of the Web page at www.mcpmag.com; other numbers are scattered all over heck and creation.
This was first published in April 2002